1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to protecting digital contents, and more particularly, to decrypting contents using a revocation mechanism, and decryption support.
2. Description of the Related Art
Recently, a rapidly increasing amount of digital content has been transmitted using various communications mediums such as the Internet, terrestrial networks, cable networks, and satellites. In addition, the sale and rental of digital contents using large-capacity recording mediums such as compact disks (CDs) and digital versatile disks (DVDs) have dramatically increased. Accordingly, digital rights management (DRM), a method of protecting copyrights of digital contents, is emerging as an important issue. Among DRM related technologies, a broadcast encryption scheme has been actively studied. In the broadcast encryption scheme, digital contents broadcast using a recording medium, such as a CD or a DVD, or the Internet are encrypted to protect the digital contents.
The broadcast encryption scheme generally uses a conventional revocation mechanism which encrypts contents using a content key and encrypts the content key using a revocation key for managing the revocation of, for example, a device or an application program, or encrypts a broadcast key used to encrypt the content key. Therefore, a device or an application program must have an identifier (ID) of a corresponding node and a revocation key set to decrypt the contents encrypted according to the broadcast encryption scheme. To decrypt the contents encrypted according to the broadcast encryption scheme, the device or the application program must also perform a decryption process. In other words, the device or the application program must receive a key block, examine whether the device or the application program has been revoked based on the received key block, and decrypt the encrypted content key. However, such a decryption process imposes a severe burden on the device or the application program when its data storage capacity is small or when its data processing capability is low.